I don't know, I'm getting bored of seeing the same old drama recommendations. I kinda want to see a drama with a villain's perspective or a mentally ill person like a psychopath. Any ideas? And it wouldn't hurt if he was hot ;)

Ghost- One of the better Kdrama villains.
Gaksital- We see the transformation from kindhearted person to near-insane villain.
Gap Dong - Lee Joon ft. his creepy smile is the hot psycho villain you want.

White Christmas - I can't say much without spoiling... But it does have a good villain.

Last Friends - domestic violence, stalking and manipulation... Yeah. One of the main characters has problems.

Also, I second Gaksital.

The Devil - the main character  is the villain  , mind that there is a little to none romance in this drama and it's quite psychologically brutal.
Queen Seon Deok definitely . Mishil is still the best villain kdramaland has ever created . Iconic
I second The Devil and Queen Seon Deok, and would also recommend Liar Game (the Korean version) and A Man's Story if you're looking for compelling psychopathic/sociopathic villains.
Well Queen Seon Deok is not from the villain's perspective but you gotta admit Lady Mishil is the best of the bestest in villain history. She's one you can only respect because she's not just wicked, she's smart, classy, awesome...even Seon Deok learns from and respects her lol.
First, I also second Gaksital (kind guy becomes bad and bad guy becomes good) and Queen Seon Deok for Mishil character.

And I'll also recommand Guilty Akuma to Keiyakushita Onna. In this one, the main character is a serial killer... falling in love with the policeman trying to catch her. I don't watch many japanese dramas but this is one of my all time favourites.

Oh and Death Note is a must, with its sequel of course. That's a movie by the way, not a drama. There's also the anime if you want.
IRIS
Black and White
Well these are movies but were absolutely brilliant with a psycho as a lead character; Aku no kyoten (Lesson of the Evil), Hwayi A monster boy, Brain man (No otoko). I loved all of these. 
Also i would suggest the japanese version of Liar Game over the Korean simply because Matsuda Shota plays the lead character so well. He's the good guy but so devilish :)
White Christmas and Seonam Girls High School Investigators. The main focus of the show isn't the villain but they're both very mentally unstable, I guess.
KING2heart , he is not hot(the villain ) but you have lee seung gi  as a lead a southkorean  prince and a north korean special agent in modern time  its action based but the love is fucking strong back to the villain  he is mentally ill or look like he is mentally ill , he is like an adult baby , psychopath ,loves war and bombs are games to him its interesting 

missing, /i miss you,  its romance mostly but its kinda of a melodrama with an happy ending, the second male lead , is a psychopath hot psychopath u hate to love him and love to hate him  even though he is kinda evil i pity him  he has a backstory although he is not the only villain he will become the main one  didn't u say u want HOT??       <Yoo Seung-ho>  nuff said
Someone already posted my suggestion, but I'll say it again. White Christmas. You want a pyschopath villain, you got one LOL

I also think "I Can Hear Your Voice" has a very interesting villain who gets a LOT of screen time especially towards the middle/end of the drama.
La Dolce Vita 
Golden Empire also has some pretty villainous characters